Roll through method for electro coating can ends

ABSTRACT

A PROCESS AND APPARATUS FOR CONVEYING ROUN, METAL PARTS HAVING RAW EDGES THROUGH AN ELECTROCATING BATH WHILE MAINTAING ROLLING, WIPING, ELECTRICAL CONTACT BETWEEN THE PARS AND A GROOVED ELECTRODE RAIL OR WHEEL.   THE PROFILE OF THE GROOVED ELECTRODE IS SHAPED TO MAINTAIN THE CONTINUOUS ROLLING, WIPING, ELECTRICAL CONTACT AGAINST THE RAW EDGE OF THE METAL PARTS.

Sept. 18, 1973 LE ROY LANDAUER ET AL 3,759,810

ROLL-THROUGH METHOD FOR ELECTROCOATING CAN ENDS 3 Sheets-Sheet 1 FiledMarch 29, 1971 US. Cl. 204-181 6 Claims ABSTRACT OF THE DISCLOSURE Aprocess and apparatus for conveying round, metal parts having raw edgesthrough an electrocoating bath while maintaining rolling, wiping,electrical contact be tween the parts and a grooved electrode rail orwheel. The profile of the grooved electrode is shaped to maintain thecontinuous rolling, wiping, electrical contact against the raw edge ofthe metal parts.

BACKGROUND OF THE INVENTION The instant invention relates toelectrocoating, and more particularly to electrocoating resin-coated,metal parts such as container ends having raw (i.e., uncoated) edges.Electrocoating is the electrodeposition of resinous coating materials,such as paint materials, from water base solutions, suspensions ordispersions. In the case of anodic coating materials, the coating ionsor particles carry a negative charge in the water base bath. These ionsor particles migrate to and discharge onto any positively charged metalwhich may be immersed in the coating bath. In the case of cathodiccoating materials, the coating ions or particles carry a positive chargein the water base bath, and these ions or particles migrate to anddischarge onto any negatively charged metal which may be immersed in thecoating bath.

Heretofore, can ends used in the packaging of beer, carbonated beveragecans and other corrosive products have been protected from attack by theproduct by a double coat system which includes a base coat which isapplied to the metal stock while it is in the flat state, usually in aroller coating operation, and by a top coat which is applied to thefabricated end by a spraying operation to seal any discontinuities inthe base coat. This top coat usually is an overall coat, since thelocation of the discontinuities cannot be precisely and reliablyascertained.

While the two coat system has generally been satisfactory, it does havea number of disadvantages in that the top coat is relatively difficultto apply at high speeds because of the problems which are usuallyassociated with spraying machines. These problems include, inter alia,the contamination of machine parts because of overspray, the need forfrequent cleanups and adjustments of the spray heads, and the need tobake the finished ends to drive off the solvent in the top coat. Theseand other problems were partially solved by the process ofelectrocoating, as disclosed in copending U.S. application Ser. No.842,461, filed July 17, 1969, now abandoned by Le Roy Landauer.

In order to positively or negatively charge a metal object to beelectrocoated, it is necessary to electrically contact the object. Thisis usually accomplished with hangers or clamps whereby one or moreindividual objects to be coated are hung or clipped to one or moreindividual hangers or clips. See said copending Landauer application.The clips or hangers are sometimes connected into groups to form racksfor hanging groups of parts. These hangers or clamps can then beautomated and conveyed for moving the parts into and out of theelectrocoating bath. Such United States Patent "ice hanging devices havegreat disadvantages when a very high speed, high volume electrocoatingoperation is required, as in the case of manufacture of can ends.

The major problem is the size and complexity of a highspeed machinewhich must clamp each end individually for electrical contact andconveyance through an electrocoating bath. The problem is furthercomplicated by the fact that any clamp, hanger, or other powertransmission device which is allowed to touch the electrocoating bathwill itself be electrocoated wherever bare metal is immersed. Thiscauses insulation of the power transmission device and can result inelectrical contacting problems with the parts to be processed throughthe electrocoating bath.

In electrocoating a resinous coating, the material being coated onto thesubstrate becomes an insulator for the substrate. In electroplating, thecoating material is a metal, which is conductive and therefore presentsno particular problems in maintaining electrical contact during aroll-through process, such as: are described in US. Pats. Nos. 1,475,198and 1.079,427. However, a rollthrough method of electrocoating aresinous coating presents .the unique problem of continuously keepingsome part of the substrate end free of coating so that said part can beutilized for electrical contact with the electrode while the substraterolls partially immersed through the electrocoating bath.

SUMMARY OF FHE INVENTION Can ends blanked from stock whether or notcovered with a base coat offer a raw, metallic edge which iselectrically conductive, and capable therefore of being used to maintainwiping, electrical contact between an electrode and the rolling can end.Thus, by utilizing the raw edge of the can end produced by the blankingoperation and by using a grooved electrode to wipe the raw edgeessentially free of the coating material at the contact point, theproblem of maintaining electrical contact inv a continuous, roll-throughelectrocoating process solved, whether or not the edge be somewhat curedunder. The surfaces of the end may be coated, while the raw edges areused for electrical contact. The fact that the edges are not well coatedis immaterial as regards the final container shape and contents therein,because the contents never see the edges, and the edges, being buriedunder a seam, are not visible to the observer.

The instant invention provides a roll-through method and apparatus forelectrocoating round, metal parts having raw edges. The inventioncomprises simultaneously rolling round, metal parts having raw edgesbetween aligned grooves of a charged electrode rail situated above anelectrocoating bath containing a resinous, organic coating material anda non-conducting guide member immersed in the electrocoating bath,maintaining rolling, wiping, electrical contact between said electroderail groove and the raw edges of said parts, and partially immersingsaid parts in said electrocoating bath for a time sufficient to rotatethe desired surface areas of the parts through the bath. The resinouscoating is deposited as D.C. current passes through the coating bathbetween the parts in contact wtih the non-immersed electrode rail and asecond electrode immersed in the bath.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical, sectional viewof a belt system used to electrocoat container ends.

FIG. 2 is a sectional view taken on the vertical plane indicated by theline 22 of FIG. 1.

FIG. 3 is an enlarged, fragmentary section of FIG. 2 showing the wipingelectrical contact between the container end raw edge and the electroderail overhead.

FIG. 4 is a sectional view taken on the vertical plane indicated by theline 44 of FIG. 1.

FIG. 5 is a vertical, sectional view of an alternative embodiment of theinvention showing a wheel-rail electrocoating system.

FIG. 6 is a sectional view taken on the vertical plane indicated by theline 6-6 of FIG. 5.

FIG. 7 is an enlarged, fragmentary section of FIG. 6 showing the wiping,electrical contact between the raw edge of the container end and theelectrode wheel.

FIG. 8 is a vertical, sectional view of a third embodiment of theinvention.

FIG. 9 is a sectional view taken on the vertical plane indicated by theline 9-9 of FIG. 8, and shows how the end is held in contact with theelectrode wheel by means of a resilient material such as black gumrubber tubing.

FIG. 10 is a fragmentary section of FIG. 9 showing the black gum rubbertubing without an end impressed therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, theround, metal part being electrocoated is a container end, generallydesignated 21, made from metal stock usually in the form of large, flat,rectangular sheets, or long coils or webs. The stock may be formed ofany suitable metal such as aluminum, aluminum alloys or any of thevarious types of steel plate used in the can making industry, such astin plate, TFS (tin free steel), black plate, etc. The sheets or coilsare then fed into the bite of a pair of coating rollers which apply anorganic resin material to one or both surfaces of the sheet or coil toform a base coat which functions as the primary barrier to seal andprotect the metal stock from corrosion.

The base coat is composed of any suitable organic coating which willadhere strongly to the surfaces of the metal stock and will provide thedesired protection thereto. There are a number of types of suitablecoatings, including phenol type coatings such as are described in UJS.Pat. 2,917,481 epoxy coatings such as are described in US. Pat.2,713,565, and vinyl polymer type coatings such as are described in US.Pat. 3,268,620. However, the invention is not limited to any specificformulation of base coat.

The sheets are then fed into an end forming press, not shown, whereinsuitable gang blanking and forming punches and dies cut circular blanksfrom the sheets and simultaneously form each blank into a basic end 21having a started flange 23, a countersink wall 25, a reinforcing groove27, and a flat, central panel 29 (FIGS. 2 and 7), all of which areprotected on both sides with the base coat. As a result of the blankingoperation, the basic end 21 has a raw, uncoated edge 31 (FIGS. 3 and 7).

During the various operations required to produce the end, especially inthe case of easy-open ends, the base coat is subject to variouspressures and abuses which frequently produce small discontinuities init with the result that the metal immediately below or adjacent thediscontinuities is exposed. Unless provision is made to treat and sealall the discontinuities, the ends cannot be used in commercialproduction since the exposed metal may adversely affect the quality ofthe contents of the filled cans.

In accordance With the present invention, the discontinuities are sealedby a roll-through electrocoating operation which deposits a sealing orrepair coat only on those surfaces of the end wherein the metal surfaceof the end is exposed because of the presence of the above describeddiscontinuities in the base coat. Of course, this same electrocoatingoperation could also be used to apply a base coat to uncoated can ends.

As the first step in the repair operation, the end is often treated toremove from its surface any oil or wax which may have been deposited onit during the previously described manufacturing operations. Suchmaterials are frequently utilized to facilitate the feeding and formingof the parts, and often form a film on the finished end.

Referring now to FIGS. 1-4 for a preferred embodiment, the ends 21 arerandomly fed through a free fall chute 33 to the electrocoatingequipment which generally comprises a belt system 35, and anelectrocoating bath 37 contained within walls generally designated 39. Afirst, angled, groove 41 of a fixed charged electrode rail 43 isvertically aligned with a second groove 45 in a moving, non-conductiveendless belt 47. The grooves are adapted to tightly hold the raw edge 31of the can ends 21 so that the edges make rolling, wiping, electricalcontact with electrode rail 43. The endless belt 47 is driven by wheel49 which is rotated by conventional energizing means not shown. The pathof the endless belt 47 is defined by drive wheel 49 and guide wheels 51,53, 55, 57 and 59. Leaf springs, generally designated 61, back up thelower portion of endless belt 47 to keep it taut and thereby tightlyhold the raw edge 31 of the can ends 21.

As best seen in FIG. 1, the electrode rail 43 and endless belt 47 guidethe can ends 21 into the bath 37, whose height is indicated by brokenline 63. The ends 21 are partially immersed in the bath 37 to a depth atleast equal to /2 their diameter, for a time sutficient to rotate theentire surface area of the ends through the bath. Following partialimmersion, the ends 21 are removed via takeoff belts 65.

As seen in FIG. 3, the electrode groove 41 is profiled so that the end21 wipes its own contact edge 31 clean as it rolls through the groove41. The electrodeposited coating which is wiped off into the groove 41by the rolling end 21 is never baked, and thus remains uncured and soft,and is easily wiped aside by each passing end 21. Provision forperiodically or continuously cleaning the groove is helpful.

The electrocoating bath 37 may be a solution, emulsion or dispersion ofa suitable, organic, coating resin in deionized water. A number ofdifferent types of electrocoat resins may be used, some of which aredescribed in US. Patent 3,230,162, granted Jan. 18, 1966, to Allan E.Gilchrist. One such coating found to be quite satisfactory is an acrylicresin of the general type disclosed in the Gilchrist patent. Preferably,a thin solution of resin, generally on the order of 2% or less resinsolids to 98% or more deionized water, is used to minimize the amount ofresin solid carried out by the end as it exits from the bath.

The end 21 is made the anode (FIG. 2) by being connected to the positiveside of the D.C. power source 67 through the electrode rail 43. Acathode 69 is immersed in the bath 37, so that when an end 21 isimmersed in the anodic coating bath 37, electrical current flows betweenthe cathode 69 and those portions of the ends 21 which are exposed tothe bath 37. Such exposed portions comprise all the discontinuities inthe base coat as well as the raw edge 31.

As the current flows, the ionized resin solids in the bath 37 aredeposited in the discontinuities on the ends 21, thus creating unbrokenprotective coatings on the ends 21. Since no electrical -fiow occurswhere the cured base coat is unbroken, no resin is deposited on thecured base coat, unless said base coat is electrically conductive, whichis not usually the case.

The thickness of the deposited resin is determined by thecharacteristics of the electrocoating bath, the voltage used, and theduration of the electrocoating operation. Preferably, the thickness ofthe repair resin is somewhat greater than that of the original basecoat, desirably about 1 /2 times as thick. A voltage of about -500volts, preferably about 200-400 volts, has been found satisfactory.

Using a typical carboxylic acid resin type coating with a 2% solid bath,2 inch diameter steel, easy-open ends were electrocoated in a 100 F.bath at 400 volts D.C. drawing 2 amps of continuous current at the rateof 200 ends per minute.

Because only about /2 of the can end is immersed in the bath at anygiven time, about 1 second of time in the bath is required to roll theentire end through 1 revolution. However, 2 revolutions are recommendedto assure sealing of all discontinuities. Usually this rate issubstantially faster than that for completely electrocoating acomparable thickness where the base coat is absent, since a completecoating deposited that quickly would not have a commercially acceptableappearance. Appearance is not a factor in the repair coat, however,since the amount of resin deposited is minimal, and its surface area isso small as to be virtually unnoticeable when the electrocoating resinis selected to have the same general appearance and coloration as thebase coat.

As the resin is deposited on a substantial number of ends, the supply ofresin in the bath 37 must be replenished.

As each end 21 is removed from the bath 37, it drags out with it some ofthe bath 37 in the form of droplets on the base coat. In order toprevent spotting of the end when these droplets dry out, the end isflushed (not shown) with a clear water rinse to remove the droplets. Theelectrodeposited resin, which contains less than 5% water, is insolublein water and tightly adhered to the end 21, is not washed off duringthis rinsing operation.

Further processing is well known to those skilled in the art of canmaking, and thus is not described herein.

The resultant product is a finished end which is completely protected bya continuous coating system which comprises the base coat and the repaircoat. The raw edge 31 is fully protected, except possibly at the area ofelectrical contact between it and the electrode rail 43.

FIGS. 5-7 illustrate an alternative embodiment of the present invention.Referring now to FIG. 5, the ends 21 are randomly fed through a freefall chute 33' to the electrocoating equipment, which in this embodimentcomprises a rotating inner wheel 81 driven by a power source not shown,a fixed, arc-shaped outer rail 83, and an electrocoating bath 37contained within walls generally designated 39. In this embodiment, theends 21 make rolling, wiping, electrical contact with the wheel 81 andare held in such contact by employing a resilient material for the outerrail 83. The end 21 functions as an anode, and a cathode 69 is immersedin the bath 37, so that current may flow from D.C. power source 67through cathode 69, end 21, and wheel 81. As seen in FIG. 7, groove 85is not angled, because the rail 83 has a groove comprising a resilientmaterial to hold the can ends 21. A doctor blade 87 is employed tocontinuously wipe clean the wheel groove 85.

FIGS. 8-1O show a third embodiment, which is similar to that shown inFIGS. 5-7 with the exception of fixed, arc-shaped, outer rail 83', whichis not resilient, and the groove 91 which is angled and accommodates aresilient material such as black gum rubber tubing 93 to hold the ends21 in contact with the electrode wheel 81'.

The round metal part may comprise almost any design imaginable. A commonexample is that of car wheels, which today are frequently subject toelectrocoating. Wheels, however, offer not only raw edges, butcompletely raw surfaces, since they are not covered with any base coats.

The depth of immersion may be /2 or more the diameter of the round partif it is desired to expose the entire surface area of the part to thebath, or it may be less than /2 of the part diameter if it is desired toexpose only certain portions of the part to the bath.

The grooves of the electrode rail and guide member are preferably invertical alignment, but any alignment desired may be used.

It is thought that the invention and may of its attendant advantageswill be understood from the foregoing descirption and it will beapparent that various changes may be made in the form, construction andarrangement of the parts of the article and that changes may be made inthe steps of the method described and their order of accomplishmentwithout departing from the spirit and scope of the invention orsacrificing all of its material advantages, the form hereinbeforedescribed being merely a preferred embodiment thereof.

What is claimed is:

1. A method of electrocoating round, metal parts having raw edges with aresinous, organic coating which comprises simultaneously:

rolling said parts between aligned grooves of a charged,

electrode rail situated above an electrocoating bath containing saidresinous, organic coating material and of a non-conducting guide memberimmersed in said electrocoating bath;

maintaining rolling, wiping, electrical contact between said electroderail groove and the raw edges of said parts; and

partially immersing said parts in said electrocoating bath for a timesufiicient to rotate and desired surface area of the parts through thebath.

2. The method of claim 1 wherein said parts are container ends, the endsare immersed to a depth at least equal to /2 the diameter of said ends,and the desired surface area is the entire surface area.

3. The method of claim 2 wherein the grooves are vertically aligned.

4. The method of claim 3 wherein the electrode rail is a rotating, innerwheel which effects the rolling of said ends, and the non-conductingguide member is a fixed, arc-shaped, outer rail.

5. The method of claim 3 wherein the electrode rail is stationary andthe non-conducting guide member is a moving endless belt effecting therolling of said ends.

6. The method of claim 5 wherein said container ends are essentiallycovered with a base coat of a resinous, organic coating.

References Cited UNITED STATES PATENTS 3,476,666 11/1969 Bell et al.204-181 3,647,675 3/1972 Fiala 204-481 HOWARD S. WILLIAMS, PrimaryExaminer US. Cl. X.R. 204-300

